1. Technical Field of the Invention
The present invention relates to a contra-rotating propeller marine propulsion device.
2. Description of the Related Art
A contra-rotating propeller is a propeller system in which the rotational energy output from a front propeller is recovered by a rear propeller, which rotates in a direction opposite to the front propeller and changed into a propulsive force so that high propeller efficiency is obtained. Hereinafter, a marine propulsion device equipped with a contra-rotating propeller is referred to as a “contra-rotating propeller marine propulsion device.” The contra-rotating propeller marine propulsion device is disclosed in the following Patent Documents 1 and 2, for example.
As one of conventional examples of the contra-rotating propeller marine propulsion device, the “propulsion device of ship” disclosed in Patent Document 1 is shown in FIG. 1. In FIG. 1, a propulsion device 100 of a ship is adapted such that an inner shaft 102 and an outer shaft 101 are concentrically disposed, a rear propeller 104 is attached to the inner shaft 102, a front propeller 103 is attached to the outer shaft 101, the inner shaft 102 is rotationally driven by a main engine 105, such as a diesel engine or a gas turbine serving as a first driving unit, and the outer shaft 101 is rotationally driven by a main engine 106, such as a diesel engine or a gas turbine serving as a second driving unit. In addition, reference numeral 107 designates a driving shaft of the main engine 106, and reference numeral 108 designates a gear transmission unit.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-67436    [Patent Document 2] Japanese Patent Application Laid-Open No. 7-33084
In the contra-rotating propeller, the inner shaft is thinner and longer than the outer shaft. Therefore, it is possible sufficiently absorb the influence of the change of hull deformation on the shaft center. However, in the outer shaft itself, which is thicker than the inner shaft, it is difficult to sufficiently absorb the influence of the change of hull deformation on the shaft center. In the conventional contra-rotating propeller marine propulsion device described above, the influence of the change of hull deformation on the shaft center of the outer shaft is not taken into consideration. Accordingly, it is desired to solve such a problem.